The present invention is in the fields of improvement technologies in a malfunction diagnostic apparatus for an internal combustion engine of a vehicle. In particular, the present invention related to a malfunction diagnostic apparatus for an evaporated fuel purge system of an internal combustion engine, intended to release an evaporated fuel from a fuel tank into an intake system during a given engine operating period in order to burn up it in a combustion chamber of the engine.
In recent years, automobiles with an engine using a liquid fuel such as gasoline have been equipped with an evaporated fuel purge system adapted to depollute an evaporated fuel generated in a fuel tank by burning it in a combustion chamber of the engine so as to comply with a demand for preventing the evaporated fuel from being released into atmosphere. The evaporated fuel purge system is typically operative to temporarily absorb and hold the evaporated fuel from the fuel tank in a canister and then separate the absorbed fuel from the canister to release it into an engine intake system under a given engine operating condition, so that the evaporated fuel generated in the fuel tank is burnt and depolluted in the combustion chamber.
Further, some evaporated fuel purge systems are provided with a malfunction diagnostic apparatus for diagnosing the presence of an undesirable leakage in the purge system, for example, as disclosed in Japanese Patent Laid-Open Publication No. Hei 11-336620. This malfunction diagnostic apparatus employs a technique in which a certain pressure is applied to a purge line between a fuel tank and a purge valve to diagnose the presence of the leakage therebetween. More specifically, a pressurized air is supplied from an electric pump or motor-driven pump to the purge line through a reference orifice having a reference diameter to pressurize the purge line. Under this state, a load current value of the motor-driven pump is measured to determine a criterion. Then, a pressurized air is supplied from the motor-driven pump to the purge line with bypassing the reference orifice to pressurize the purge line. At that moment, a load current value of the motor-driven pump is measured and compared with the criterion to diagnose the presence of the leakage in the purge line. For example, if the purge line has a certain leakage greater than that caused when an aperture equivalent to the reference orifice is generated in the purge line, the load for the pressurization will be reduced and thereby the load current value of the motor-driven pump becomes smaller than the criterion. In this manner, when the load current value is smaller than the criterion, it is determined that there is a leakage in the purge line.
The above malfunction diagnostic apparatus is operable to diagnose the presence of a leakage in the purge line or the line between the fuel tank and the purge valve. However, the above malfunction diagnostic apparatus has a disadvantage in that it cannot comply with the demand for diagnosing multifunction in looseness, clogging or the like of piping between the purge valve and the engine intake passage.
In view of the above problem of the conventional malfunction diagnostic apparatus for the evaporated fuel purge system, it is therefore an object of the present invention to provide an improved malfunction diagnostic apparatus for an evaporated fuel purge system capable of detecting any malfunction in looseness, clogging or the like of piping between the purge valve and the engine intake passage.
In order to achieve the above object, according to the present invention, there is provided a malfunction diagnostic apparatus for an evaporated fuel purge system for use in an internal combustion engine, wherein the evaporated fuel purge system includes an evaporated fuel purge line ranging from a fuel tank to an intake passage of the engine, and a purge valve provided in the purge line and adapted to be selectively switched to either one of an open state for allowing the fuel tank to be in gaseous communication with the intake passage and a closed state for preventing the fuel tank from being in gaseous communication with the intake passage. The malfunction diagnostic apparatus comprises: pressurization means for supplying a pressurized air to a first zone of the purge line between the fuel tank and the purge valve; drive means for driving the pressurization means; diagnosis means for diagnosing the presence of a leakage in the first purge-line zone in accordance with a driving load value caused in the drive means during supplying the pressurized air from the pressurization means when a given diagnostic condition is satisfied and the purge valve is in the closed state; and gaseous-communication-state determination means for determining a gaseous communication state in a second zone of the purge line between the purge valve and the intake passage in accordance with the driving load value at the moment after the lapse of a given time period from the time the purge valve is switched from the closed state to the open state, with driving the pressurization means during a given engine operating period. As above, the malfunction diagnostic apparatus according to the present invention includes the gaseous-communication-state determination means operable to detect the gaseous communication state in the second purge-line zone between the purge valve and the intake passage in accordance with the driving load value during supplying the pressurized air from the pressurization means when the purge valve is in the closed state. Thus, in addtion to the diagnosis of the presence of a leakage in the first purge-line zone by the diagnosis means, the normality and abnormality of the gaseous communication state in the second purge-line zone can be reliably detected.
In a first preferred embodiment, the malfunction diagnostic apparatus according to the present invention may further comprises a gaseous communication passage for providing gaseous communication between the pressurization means and the first purge-line zone. The gaseous communication passage includes a first passage having a reference orifice interposed therein, a second passage bypassing the reference orifice; and a shutoff means adapted to be selectively switched to either one of an activated state for shutting off the second passage and a deactivated state for opening the second passage. In this case, the gaseous-communication-state determination means is operable to detect a first driving load value in the drive means at the moment when the shutoff means is switched from the activated state to the deactivated state with the purge valve being in the closed state, and detect a second driving load value in the drive means at the moment after the lapse of a first given time period from the time the purge valve is switched to the open state at the moment after the lapse of a second given time period from the switching operation of the shutoff means, so as to determine the gaseous communication state in the second purge-line zone between the purge valve and the intake passage in accordance with the relationship between the first and second driving load values. According to the above construction, the gaseous-communication-state determination means can determine if the second purge-line zone has malfunctions of the gaseous communication state in accordance with the first and second driving load values. This allows adequate action to be promptly taken to such abnormalities.
The above gaseous-communication-state determination means may be operable to determine that the second purge-line zone between the purge valve and the intake passage is clogged, when the second driving load value is greater than the first driving load value, and the difference between the first and second driving load values is equal to or greater than a given value. According to this construction, the gaseous-communication-state determination means can determine if the second purge-line zone is clogged in accordance with the first and second driving load values.
The gaseous-communication-state determination means may also be operable to determine that the second purge-line zone between the purge valve and the intake passage is wrongly opened to atmosphere, when the second driving load value is greater than the first driving load value, and the difference between the first and second driving load values is less than a given value. According to this construction, the gaseous-communication-state determination means can determine if the second purge-line zone is wrongly opened to atmosphere (for example, due to the looseness of piping) in accordance with the first and second driving load values.
Further, the gaseous-communication-state determination means may be operable to determine that the gaseous communication state in the second purge-line zone between the purge valve and the intake passage is normal, when the second driving load value is equal to or less than the first driving load value.
In the first preferred embodiment, the malfunction diagnostic apparatus may further comprise an air-fuel ratio detecting means for detecting a value associated with air-fuel ratio, and an air-fuel ratio feedback means for performing a feedback control to match an actual air-fuel ratio with a desired air-fuel ratio in accordance with a detection result of the air-fuel ratio detecting means. In this case, the gaseous-communication-state determination means is operable to determine that the gaseous communication state in the second purge-line zone between the purge valve and the intake passage is normal, when the second driving load value at the moment after the lapse of the first given time period is equal to or less than the first driving load value at the moment when the shutoff means is switched to the deactivated state, and a air-fuel ratio feedback correction value in the air-fuel ratio feedback control at the moment after the lapse of the first given time period from the switching operation of the purge valve is equal to or greater than a given value. According to the above construction, the normality of the gaseous communication state in the second purge-line zone can be determined in accordance with the detection of the normality in the gaseous communication state by the gaseous-communication state determination means and the detection of the transition to rich-side in air-fuel ratio by the air-fuel ratio detecting means. This allows the normality of the gaseous communication state to be detected with higher level of accuracy.
In a second preferred embodiment, the malfunction diagnostic apparatus according to the present invention may further comprise a gaseous communication passage for providing gaseous communication between the pressurization means and the first purge-line zone. The gaseous communication passage includes a first passage having a reference orifice interposed therein, a second passage bypassing the reference orifice, and a shutoff means adapted to be selectively switched to either one of an activated state for shutting off the second passage and a deactivated state for opening the second passage. In this case, the diagnosis means is operable to diagnose the presence of a leakage in the first purge-line zone between the fuel tank and the purge valve in accordance with the relationship between a first driving load value in the drive means at the moment when the shutoff means is switched from the activated state to the deactivated state, and a second driving load value in the drive means at the moment after the lapse of a given time period from the switching operation of the shutoff means. According to the above construction, the diagnosis means can specify conditions for diagnosing the presence of the leakage in the first purge-line zone. This allows the presence of the leakage in the first purge-line zone to be diagnosed with a high level of accuracy.
The above diagnosis means may be operable to diagnose that the first purge-line zone between the fuel tank and the purge valve includes a relatively small leakage, when the difference between the first and second driving load value at the moment after the lapse of a first given time period from the switching operation of the shutoff means is equal to or less than a first given value. The diagnosis means may also be operable to diagnose that the first purge-line zone between the fuel tank and the purge valve includes a relatively small leakage, when the difference between the first and second driving load value is greater than a first given value, and the difference between the first driving load value and a third driving load value at the moment after the lapse of a second given time period from the switching operation of the shutoff means is equal to or less than a second given value greater than the first given value, the second given time period being greater than the first given time period. In addition, the diagnosis means may be operable to determine that the second purge-line zone between the purge valve and the intake passage is normal without any leakage, when the difference between the first and second driving load value is greater than the second given value. According to the above constructions, the diagnosis means can variously diagnose the normality and abnormality in terms of leakage in the first purge-line zone. This allows the presence and level of the leakage in the first purge-line zone to be diagnosed with a high level of accuracy.